As modern aircraft, particularly military aircraft, require greater and greater cooling to absorb heat from avionics and particularly radar, the trend is toward more use of liquid coolant to transfer heat from the avionics, and even the cabin, to cold air from the air conditioning system.
A conventional method for accomplishing such cooling is an open-loop air cycle cooling system which supplies cooled air from a turbine to cool liquid coolant which is associated with a cooling system for electronics such as radar. Heat exchange between the liquid and cold air occurs in a liquid/air heat exchanger, but a principal limitation in efficiency exists in the maintenance of above-freezing conditions in the cold air flow path to prevent ice buildup at the liquid heat exchanger. The air cycle turbine flow must be reheated above freezing to prevent icing of entrained water in the flow path; this reheating diminishes the air cycle system's cooling capacity.
A conventional solution to this problem is to create an anti-ice bypass around the air cycle turbine and compressor, such bypass channeling hot air to mix with turbine exit air, controlled to 40.degree. F. or more. The utilization of a substantial bypass represents a parasitic load and in general decreases the efficiency of the process, resulting in more engine bleed air usage.